This invention relates to articulated trailers (such as those which transport material in open-cut mines) adapted for trailing off-road for transporting bulk material and being larger than trailers which are permitted to operate on public road systems.
This invention has particular but not exclusive application to bulk-haulage trailers for coal and other minerals, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as scrapers and other articulated vehicles.
A bulk materials haulage trailer typically comprises a rectangular bottom discharge hopper to the rear of which an axle assembly is attached, and to the front of which a hitch assembly is attached for connection to a prime mover. The hopper is made as wide as is practicable to maximise payload, and the side plates of the hopper are essentially deep-beam members which carry the main bending loads due to the weight of the trailer and its payload.
The major structural problem facing the designer of such a trailer is the transfer of the loads from the widely-spaced side plates to the trailer hitch, which is mounted on the longitudinal centerline of the vehicle. It is known that the fatigue life of welded joints is much lower than that of the parent metal for a given applied stress regime, and that certain weld configurations, including welds made from only one side of a joint, are more susceptible to fatigue failure than welds of simple configuration, or where the welds are accessible from both sides. Various structural configurations are in use on existing vehicles to effect this load transfer, but many are excessively heavy for their capacity, while others contain regions of high stress such that welds employed in the joining of the various plates used to form the structure may be the subject of metal fatigue early in the life of the vehicle. Where the structural configuration includes a pair of main beams extending rearwardly from the trailer hitch and diverging transversely to connect with the front ends of the side plates, the front end of the hopper is subjected to bending moments about longitudinal axes, otherwise known as a transverse bending moment component. The presence of this bending moment can lead to structural failures, or the necessity for making the hopper excessively heavy to resist the moments.